Actually... none of those. DPN (double pointed needles) are way too short.. a 16" circular only fits a hat really and the 10" are too short as well as awkward with a large project.
A blanket can be a large project that is usually best suited to circular needles. The length depends on the size of blanket.. a baby one might be able to be done on a 32", but I'd say go for a 40" to be comfortable. It's somewhat of a personal choice though.